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A307758 Average of twin prime pairs that is a product of two averages of twin prime pairs. 2
72, 108, 180, 240, 432, 600, 828, 1152, 1620, 1872, 2088, 2592, 3528, 3852, 4128, 4932, 4968, 5280, 6300, 6552, 6792, 7488, 7560, 9000, 9240, 9720, 10008, 10332, 11160, 11700, 12240, 13008, 13680, 15288, 16632, 18540, 20232, 20772, 20808, 21492, 25308, 25800, 26892 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
All terms == 0, 24, 36 or 48 (mod 72). - Robert Israel, Apr 30 2019
LINKS
EXAMPLE
108 = 6*18. 6 and 18 are both averages of twin prime pairs, so 108 is in the sequence.
MAPLE
N:= 10^5: # to get all terms <= N
P:= select(isprime, {seq(i, i=3..N+1, 2)}):
TPA:= map(`+`, P, 1) intersect map(`-`, P, 1):
R:= select(t -> ormap(d -> member(t/d, TPA), TPA intersect numtheory:-divisors(t)), TPA):
sort(convert(R, list)); # Robert Israel, Apr 30 2019
PROG
(PARI) isok1(n) = isprime(n-1) && isprime(n + 1);
isok2(n) = fordiv(n, d, if (isok1(d) && isok1(n/d), return(1)); );
isok(n) = isok1(n) && isok2(n); \\ Michel Marcus, Apr 27 2019
CROSSREFS
Cf. A014574.
Sequence in context: A308053 A356871 A359280 * A272191 A072412 A052486
KEYWORD
nonn
AUTHOR
Dmitry Kamenetsky, Apr 26 2019
STATUS
approved

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Last modified March 29 04:23 EDT 2024. Contains 371264 sequences. (Running on oeis4.)